Cases as part of ammunition both for small-bore weapons and for large-bore weapons have long since been known and are commonly used. Above all, they serve for accommodating the propellant charge powder. Usually, cases have a circular-cylindrical and oblong hollow shape; the actual sheath here is referred to as jacket wall.
For producing a shell, the case generally is additionally equipped with a bottom comprising a primer. The same usually is made of metal, mostly of steel. For producing a cartridge, a projectile additionally is placed onto the free longitudinal end of the case opposite the bottom.
Combustible cases also are known in principle. They are burnt or consumed as a result of firing. If this occurs sufficiently free from residues, no case rests must be removed before the next shot. Ideally, only the bottom has to be ejected.
For combustible cases, a combustion as free as possible from residues therefore is desirable, in order to avoid an additional cleaning of the charge space or the barrel.
It is known to produce combustible cases from nitrocellulose and cellulose; in general with additives such as binder resin and stabilizers. Conventionally, a screen mold is vertically immersed into an aqueous pulp with nitrocellulose and cellulose. By means of negative pressure, the screen mold sucks in the fibrous pulp; there is formed a wet raw felt. In principle, this material can also be referred to as “fleece”. However, the term “raw felt” has gained acceptance here. To achieve the final geometry and for dewatering, the raw felt also is compressed and heated at least at times.
The cases must have a certain mechanical stability. A small deformation may be tolerable, but there should not form a crack. Through a crack, propellant charge powder might leak—a safety risk which is not tolerated. According to some specifications, the cases therefore are designed with an additional, internally located bag for accommodating the propellant charge powder, a so-called powder bag.
The stability of the case is particularly relevant for tank ammunition, since here the requirements concerning the mechanical stability can be very pronounced, for example due to the handling within the tank and as a result of loads and movement shocks when attaching the cartridge. The invention is, however, not limited to tank ammunition.
DE 30 08 996 A1 discloses a method for producing combustible cases. It is proposed to roll fabric inlays into the raw felts during the felting operation. It was found that a case produced in this way can break up into several parts during an impact. The felt can detach from the inserted fabric over a large surface. In the worst case, the case is split into three separate parts, namely the fabric inlay and the raw felt which has detached from the inside and the outside of the fabric.
DE 36 19 960 A1 discloses a combustible case with additional reinforcements made of metal or plastics. These reinforcements can be embedded in the case or also be fixed on the same. If the reinforcements are embedded in the case, they are provided with holes, so that the rest of the case can burn through these holes. The reinforcements themselves, however, are not burnt.